Question #4

Step #1:     (62.9296) (x) + (64.9278) (1-x) = 63.546
Step #2:     62.9296x + 64.9278 - 64.9278x = 63.546
Step #3:     62.9296x - 64.9278x = -1.382
Step #4:     -1.9982x = -1.382
Step #5:     x = .692          (or x = 69.2%)

The % abundance of:
Cu-63 = 69.2%
Cu-65 = 30.8%